Real time traffic loads detection and traffic speed measurement in specific routes is an urgent and important need in the modern urban areas. Statistical data about traffic loads in different time frames is a valuable asset for municipal planning authorities as well as commercial companies (road services, fleet companies etc.)
Until now these needs are fulfilled only partially, not in real time and in a very costly manner: Airplanes in peak hours, Cameras at key locations and (inaccurate) reports of driver's experience are used to generate partial, close to real time traffic data. Counters periodically located across the road in specific locations are used to generate local and partial statistical traffic data.
These inaccurate, costly methods are being used because until the last years there were no means to accurately inexpensively locate vehicles from remote. Lately two such mechanisms were introduced:                1. The GPS system that enables accurate detection of vehicles carrying GPS location detectors, of course a communication device is required to transmit the location data to a central location for analysis. In addition since the vehicle is identified this requires the owners consent. The GPS system is being used to some extent in theft detection/emergency services applications.        2. The cellular mobile systems with an exponentially growing installed base supply location information. Some companies have explored the option to extract traffic information by sending location data from cellular phones to an analysis center. Due to the quantities of calls or data-links that are required in order to receive a complete traffic picture, this method is not relevant to cellular operators, and their systems are likely to collapse if incorporated in such a system.        
A cellular network consists of the following elements:                1. Cellular switches (typically controls 4-8 base station controllers)        2. Base station controllers (typically controls 32-64 base stations)        3. Base stations (where the cellular antennas are located)        4. Mobile units (cellular phones).        
The first 3 elements are connected mostly by physical lines while the connection to the mobile unit is achieved through the air interface.
The network includes voice/data channels and forward/backward control channels that synchronize the network operation.
When a mobile unit moves across an area, reports of the signal strength from several base station is sent periodically over the control channels.
The signal level of the currently serving base station is monitored continuously and when it decays, a handover (also known as handoff) occurs that transfers control to another base station.
While the voice/data information goes all the way from the mobile unit to the cellular switch, the information that flows on the control channels does not always reach the cellular switch. For example signal strength information reaches the base station controller only, while handover information usually reaches the cellular switch.
Several methods are known in prior art that teach location detection or traffic speed monitoring based on cellular information.
U.S. Pat. No. 5,602,903 issued to LeBlanc et al and assigned to US West Technologies teaches a method of mapping cells boundaries based on RF measurements as polygons. In order to locate a mobile unit, the polygons for all base stations per it's location are intersected to yield the bounding of the polygon area that describes the position of the mobile unit in term of a minimum and maximum error estimate. This method is inaccurate in rural areas because of the large cells and will provide erroneous positions in urban areas due to the frequent radiation blocking and reflecting elements.
U.S. Pat. No. 5,657,487 issued to Doner and assigned to Airnet Communications teaches a method of mapping an area with vectors of cellular signal strength in a certain point from several base stations and then, when a car passes through, such mapping can determine on which road this car was traveling. Since this method is based on signal strength measurements that are performed periodically, it will get conflicting measurements in case of sharp signal changes within several meters range due to RF radiation blocking/reflecting elements. Actually this method teaches how to filter such changes and ignore areas in which such changes occur (see detailed explanation within the description of the Doner invention). This makes it insufficient in dense urban areas where such sharp changes are common. Further more—a system that will collect the signal strength data from all the base stations will be very large, costly and unrealistic to implement.
U.S. Pat. No. 5,465,289 issued to Kennedy and assigned to E-systems teaches a method that uses dedicated traffic sensors (RF receivers) that monitor cellular communications within an area. When a vehicle passes through a cell the entry and exit time of the call are recorded and, knowing the length of the road within the cell, the vehicle speed is generated. This method requires a dense spread of dedicated RF receivers across the area. In addition it may work only in cases where just one road, without any junctions, passes through a cell, and thus it can't be used for urban areas, nor for junctions within a cell.
The methods described in the prior art detailed above are insufficient for high accuracy traffic speed monitoring in urban areas. They do not supply solutions to the RF radiation blocking and reflecting elements within urban areas that have a very strong influence on handovers and signal strength sharp changes when driving through an urban area. They do not take into account the fact that within an urban area several road sections may pass through the same cell and screening algorithms applied on cell sequences are required to differentiate between those roads.
In addition the implementation of the methods mentioned above involve very high costs and many unnecessary elements. The 1st two are based on signal strength measurements. Although the manner in which they extract the information is not disclosed, it may be extracted either from the lines connecting the base stations to the base station controllers or from the air interface, which requires large quantities of expensive equipment (about 10-100 times more expensive and 50 times more components relative to monitoring the communication lines between the base station controllers and the switch). Trying to send all this information through the cellular network to the cellular switch is also not practical because it will load the cellular network in a manner that will cause it to collapse. The 3rd prior art discloses an extremely expensive implementation requiring RF receivers spread over the covered area.
The current invention introduces a method to extract traffic information from any cellular network in every load stage possible, with minimal hardware elements and hence minimal system cost. This invention teaches a method to utilize the frequent and repeatable handovers caused by the radiation blocking and reflecting elements in urban areas in order to further increase the accuracy of the correlation between cars and the road they travel on, while minimizing and simplifying the system required for this, and thus provides a much better resolution needed for speed extraction in urban areas.